Industrial robot

ABSTRACT

An industrial robot is disclosed in which inertia is reduced and backlash substantially eliminated by mounting motors for the first and second movable arms on a stationary stand, and transmitting torque to the second arm by means of timing belts. A harmonic gear mechanism arranged at the juncture of the first and second arms reduces the speed of the output timing pulley. The belt arrangement requires no lubrication and is lighter and much quieter in operation than previous torque transmitting arrangements.

BACKGROUND OF THE INVENTION

This invention relates to industrial robots, and more particularly toimprovements in a horizontal articulation type industrial robot in whicha first arm is rotatably mounted on the shaft of a stationary stand anda second arm is rotatably mounted at the end of the first arm.

Conventional horizontal articulation type industrial robots are shown inFIGS. 1 and 2.

As shown in FIG. 1, a first arm 12 is rotatably mounted on a stationarystand 10, and a second arm 14 extends from the end of the first arm 12.A motor 16 for driving the first arm is provided above the stationarystand 10, and a motor 18 for driving the second arm is provided on theend of the first arm 12. The end of the second arm 14 is coupled to asuitable hand 20. In this industrial robot, the first arm 12, the secondarm 14 and the second arm driving motor 18 protrude sidewardly, and thispart of the robot is relatively large in weight. Therefore, the arms 12and 14 and the stationary stand 10 are liable to bend, and the robotitself is not suitable for high speed operations.

The industrial robot shown in FIG. 2 is an improvement of the robot ofFIG. 1. In FIG. 2, those components which have been described withreference to FIG. 1 are designated by the same reference numerals, and adescription thereof is therefore omitted.

In this industrial robot, the first arm driving motor protrudes in adirection opposite the direction of protrusion of the first arm 12, andthe second arm driving motor 18 is provided with a planet type speedreducing unit 22 and is secured to the upper surface of the first arm 12above the stationary stand 10. The output of the speed reducing unit 22is transmitted through a shaft 24 to a bevel gear 26 at the end of theshaft 24, to rotate the bevel gear. The rotation of the gear 26 istransmitted through a bevel gear 28 to a shaft 30 integral with thesecond arm 14, to turn the shaft 30 and accordingly the second arm 14.

The planet type speed reducing unit 22 may be one bearing the trademark"Harmonic Drive" of Harmonic Drive Systems Co. The unit can transmitpower from the input side to the output side at a predetermined gearreduction ratio. However, since the power transmitting mechanism employsgears, not only it is necessary to employ a gear adjusting means, butalso it is necessary to use sealing materials for lubrication.Furthermore, the mechanism suffers from problems in that the gears arenoisy and are subject to wear. In addition, the robot is disadvantageousin that the second arm 14 is liable to play owing to the backlashencountered in the use of a gear, and accordingly the accuracy ofpositioning operations is lowered, with the result that the robot cannotbe used for assembly operations of high accuracy.

In addition to the foregoing prior art, Japanese publication No.55-112789 discloses an industrial robot, wherein rotary drive mechanismsfor the first and second arms are provided on respective rotary shafts.That is, the drive motor for the second arm is disposed on the firstarm, so that the moment of inertia of the first arm is large, which isdisadvantageous in the movement of the first arm. Japanese publicationNo. 56-62778 discloses a drive motor (17) for the second arm (12). Thedrive motor is disposed at a position opposite the first arm (11) withrespect to a main sleeve (4). Further, bevel gearing is used for powertransmission to the second arm. However, speed reduction means isdisposed between the gearing and the motor, and backlash of the gearingmay affect working accuracy. Even though a desirable moving balance maybe obtainable in the device according to this publication, the moment ofinertia is large, so that high responsiveness is not obtainable.

SUMMARY OF THE INVENTION

In view of the foregoing, an object of the invention is to provide anindustrial robot in which swinging movement can be achieved at highspeed while positioning can be performed with high accuracy, and inwhich cables can be readily arranged, adjustment and lubrication are notrequired, and noise is scarcely made.

The foregoing object and other objects of the invention have beenachieved by the provision of a horizontal articulation type industrialrobot in which a first arm is rotatably provided on a stationary standand a second arm is rotatably coupled to the end of the first arm, inwhich, according to the invention, a second arm driving motor isprovided on the stationary stand at the rear of the first arm, and therotation of the second arm driving motor is transmitted through timingbelts and a planet type speed reducing unit to a shaft about which thesecond arm is rotated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are side views showing two examples of conventionalhorizontal articulation type industrial robots; and

FIGS. 3 and 4 show one example of an industrial robot according to thisinvention.

More specifically, FIG. 3 is a side view, with parts cut away, of therobot, and FIG. 4 is an enlarged sectional view of the front end portionof a first arm of the robot of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of this invention will now be described withreference to FIGS. 3 and 4. In FIGS. 3 and 4, those components whichhave been previously described with reference to FIGS. 1 and 2 aretherefore similarly numbered and the preceding descriptions thereof areapplicable.

A motor receiving box 32 is fixedly secured to the stationary stand 10.The second arm driving motor 18 is accommodated in the box 32. A timingpulley 34 is fixedly mounted on the output shaft of the motor 18. Twobearings 36 and a timing pulley 38 are arranged coaxially with therotary shaft of the first arm 12. At the end of the first arm 12, atiming pulley 44 is fixedly mounted on a shaft 42 which is suportedthrough bearings 40. A timing belt 46 in laid over the timing pulleys 34and 38, and a timing belt 48 is laid over the timing pulleys 38 and 44.The lower portion of the shaft 42 is coupled through a planet type speedreducing unit 50 to the shaft 30 which is secured to the second arm 14for rotation of the latter.

The unit 50 (trademark "Harmonic Drive") is made up of an elliptic cam52 secured to the shaft 42, an internal gear 54 fixed to the first arm12, and an elastic gear 56 secured to the shaft 30, the number of teethof the gear 56 being generally smaller by two than the number of teethof the gear 54. Thus, the rotation of the shaft 42, being reduced inspeed by the ratio of two to the number of teeth of the elastic gear 56,is transmitted to the shaft 30. The unit 50 is the same as theconventional planet type speed reducing unit 22 shown in FIG. 2.

In FIGS. 3 and 4, reference numeral 58 designates a housing whichextends downwardly from the end of the first arm 12; 60, bearingsinterposed between the housing 58 and the shaft 30; and 70, a motor fordriving a band or the like which is connected to the end of the secondarm 14.

In the industrial robot according to the invention, rotation of thesecond arm driving motor 18 is transmitted through timing belts 46 and48 and the planet type speed reducing unit 50 to the shaft 30 forrotation of the second arm 14.

The robot shown in FIG. 3 is so designed that the first arm 12 isrotatable through about 270° to 280°, while in the conventional robotshown in FIG. 1 or 2 it is rotatable through 360°. However, no practicalproblem occurs in operation, because the second arm 14 is also rotatablethrough about 270° to 280°.

The second arm driving motor 18 is provided on the stationary stand 10according to the invention. Therefore, the weight of the first arm 12can be reduced, which makes it possible to reduce the inertia thereof,and not only can be first arm 12 swirl at high speed, but also thetorque of the first arm driving motor 16 can be reduced.

The first arm driving motor 16 may be built into the stationary stand 10or may be mounted on the rear end of the first arm 12 as shown in FIG.2. However, it may be desirable to provide the first and second armdriving motors 16 and 18 on the stationary stand 10, because in thiscase the power cable and the like can be readily positioned.

Timing belts 46 and 48 are used to drive the second arm 14 as describedabove. Accordingly, when compared with a gear transmission system, theweight is small, the required space is also small, adjustment andlubrication are eliminated, and the generation of noise can beprevented.

The timing pulley 38 is provided coaxially with the rotary shaft of thefirst arm 12, and the torque of the second arm driving motor 18 istransmitted through the timing pulley 38 thus provided to the speedreducing unit 50. Therefore, no problems occur with the operations ofthe timing belts 46 and 48 even when the first arm 12 swings. This isdue to the following reason: As the timing pulley 38 is mounted on thecircumferential walls of the two ball bearings 36 which are mounted onthe rotary shaft of the first arm 12, the pulley 38 is not affected bythe rotation of the rotary shaft of the first arm 12.

The planet type speed reducing unit 50 is provided at the shaft 30 forrotation of the second arm 14 as described above. Therefore, thebacklash of the timing pulleys 44 and 38 can be substantially neglected.Accordingly, a remarkable improvement in the positioning accuracy can beobtained.

That is, in the robot of the invention, unlike conventional robots inwhich the gears are arranged at the output side of the planet type speedreducing unit, the planet type speed reducing unit is instead providedat the output side, which is in this case the rear stage of the timingpulleys and timing belts, and accordingly, backlash is decreased withspeed reduction, and is negligible.

As is apparent from the above description, in the industrial robot ofthe invention, work efficiency and positioning accuracy are improvedwhile the inertia of the moving parts is lowered as a whole.Furthermore, the robot of the invention needs no lubricating structureor lubrication as is unavoidably required by conventional robots. Thus,the industrial robot of the invention is excellent as respectsmaintenance.

What is claimed is:
 1. An industrial robot, comprising:a stationarystand which supports a shaft; a first arm rotatably mounted on saidshaft; motor receiving means fixedly secured to said stationary stand atthe rear of said first arm; speed reducing means mounted at the frontend of said first arm; a second arm secured to a second shaft coupled tothe output side of said speed reducing means; a second arm driving motorsecured in said motor receiving means and having an output shaft onwhich a first timing pulley is fixedly mounted; a first arm drivingmotor built into said stationary stand; a first timing belt laid oversaid first timing pulley and a second timing pulley which is coaxiallymounted on the end of said shaft supported by said stationary stand; anda second timing belt laid over said second timing pulley and a thirdtiming pulley mounted on a third shaft coupled to the input side of saidspeed reducing means, said second timing belt being accommodated insidesaid first arm.
 2. An industrial robot as claimed in claim 1, saidsecond timing pulley being interposed between said motor and said speedreducing unit in a torque transmission path of said second arm drivingmotor.
 3. An industrial robot as claimed in claim 1, wherein said secondand third timing pulleys are arranged inside said first arm.
 4. Anindustrial robot as claimed in claim 1, said motor receiving meanscomprises a receiving box.
 5. An industrial robot as claimed in claim 1,wherein said speed reducing means comprises a harmonic speed reducer.